Rubber preserved with thiazylthio dihydroxybenzenes



Patented Nov. 4, 1952 1r; STATES PATENT RUBBER .BRESERVED WITH THIAZYLTHIO DIH YDROXYBENZENES Thomas H. Newby, Waterbury, Conn., assignor to ,United' States Rubber Company, New York, L, a corporation of New Jersey 'No Drawing. Application April 7, 1949, y Serial No. 86,108

' ,Theprincipzfl object of the. present invention l is to. make available anew classof chemical compounds which are particularly valuable "as antioxidants. Another object is to protect organic materials, particularly natural and synthetic rubber, against the deterioration which normally .occur-s when these materials are exposed to the .action of atmospheric oxygen. Another object is to provide a non-staining and non-discoloring mantioxidant. Numerous other objects :will more fully hereinafter appear. I The chemical compoundsot the present invention are the 2-- 2-.thiazylthio) -1.4-dihydroxybenwzenes'having the en ral formula r where R and R may be hydrogen, alkyl,a1'yl, or part of a ring system. The groups R and R or the ring of which they are a part may be substituted with groups which do not interfere with the antioxidant action of the compound and which do not interfere with the formation of the compound in accordance with Equations 1 and 2 be1ow.,examples of such substituent groups being nitro .and .hydroxy as Well asalkyl such as methyl and ethyl. I

.The compounds of my invention conveniently may be. designatedv as 2-(2-thiazylthio)-hydroquinones of the benzene series.

The chemical compounds of my invention may be readily prepared by reacting a Z-mercaptothiazole with p-benzoquinone as shown by the following equation:

The reaction is typically carried out "by reacting equal molar quantities of p-benzoquinone and the 2'mercaptothiazole in an inert solvent at temperatures varying from C. to the boiling point of the solvent. After the reaction has attained the desired degree of completion, the product is recovered in any suitable manner. Typically, the reaction mixture contains a small amount of insoluble material which comprises a mixture of the desired product with some disulfide which is formed as a by-product by oxidation of some of the desired product to a quinone, part of which then combines with an additional 7 molecule of the Z-mercaptothiazole to form a disubstituted hydroquinone.

Examples of .Z-mercaptothiazoleswhich may be reacted with p-benzoquinone to yield ,compounds of the present invention includet 2-mercaptobenzothiazole "6nitro-2-rnercaptobenzothiazole *6 -hydroxy-2-mercaptobenzothiazole 14;5-dimethyl-2-mercaptothiazole 4,5sdiethyl-2 -mercaptothiazole 4-methyl-2emercaptothiazole -ethyl-Z -mercaptothiazole 5-methyl-Z-mercaptothiaZole 4-phenyl-2-mercaptothiazole 4,5-diphenyl-2-mercaptothiazole 2-mercaptothiazole While p-benzoquinone is preferably used in making the compounds of my invention, I may use lA-benzoquinones substituted in suitable positions with suitable groups which do not in- "terfere *with the antioxidant action of the co'mpound and which do not interfere'w-ith the formation of the compound in the manner described above, for example with alkyl, alkoxy, nitro, and hydroxy groups. At least one position ortho "to one of the carbonyl groups should be unsubstituted and-any substitution in other posit-ions should be such as to allow the reaction outlined above to take place and not to interfere with the antioxidant action. Possiblesubstitut'ed quinones for use in this reaction will beappar-ent to those skilled in the art. The most preferred compounds of my invention are those made from p-benzoquinone.

Examples of quinones other than .p-benzoquinone which can be used include:

2,5-ditertiarybutyl-p-benzoquinone Methoxy-p-benzoquinone 2,5-dimethyl-pbenzoquinone 3,5-dimethyl-p-benzoquinone Nitro-p-benzoquinone Hydroxy-p-benzoquinone The following examples illustrate the preparative method more fully.

Example 'I 2- (Z-benzothiazylthio) -1,4-dihydrowybenzene.Quinone (22 g.) was dissolved in 150 cc. of boiling methanol and thesolution cooled rapidly to 0-5 C. in an ice bath whereupon the 'quinone crystallized in fine needles. To this mixture a slurry of 33 g. of z-mercaptobenzothiazole in cc. of ice-cold methanol was added. The reaction mixture was then stirred for two hours at 0-5 C.

The product was isolated by filtering off the small amount of methanol-insoluble material and then quenching the methanol solution in 500 cc. of hot water. The mixture was boiled and the lumps broken up until no longer sticky. After filtration and drying 42 g. (76% yield) of crude 2 -(2 benzothiazylthio) 1,4 dihydroxybenzene melting 204.5-208 C. was obtained. After recrystallization from ethyl acetoacetate it melted 218-219" C.

Gar- Hydro- Sul- Nitro- Analysls bon gen fur gen Found 56. O1 3. 29 23. 42 5. 05 Theory for ClaHoOzNSz 56. 73 3. 27 23. 2-7 5. ()9

the precipitate, 23 g. of 2-[2-(4,5-dimethyl thiazylthio)] 1,4 dihydroxybenzene were obtained. Treatment of this material with hot methanol gave g. of a methanol-soluble solid melting 148-152 C. and a small amount of methanol-insoluble material. The yield of the methanol-soluble product was 79%.

Analysis Nitrogen Sulfur Found 5. 37 25. 59 Theory for CnHnOzNSz 5. 54 25.

Example III2-[2-(4-methyl thz'aeylthz'o) 1,4-dihydroxybenzene.Quinone (21 g.) and 4- .methyl-2-mercaptothiazole (26 g.) were reacted as described in Example II for the dimethyl body.

The product was worked up by filtering off the methanol-insoluble material (11 g. melting 239- 247 C.) and then quenching the methanol filtrate with hot water. After boiling the water solution for a short time the solids were filtered off. The product when dry Weighed 32 g. (67% yield) and melted 158-16l C. after two washings with hot benzene.

The material melting 239-247 C'. was shown by analysis to be a mixture of monoand di-substituted 1,4-dihydroxy benzene.

Any of the compounds of my invention may be employed as antioxidants for the organic substance to be protected against oxidative deteriora tion. In practice, a suitable amount of the chemical is incorporated uniformly into the material to be protected, usually by simple physical admixture in any suitable equipment. The amount used should be such as to give the desired degree of protection. Usually an amount ranging from 0.05 to 5.0 parts per 100 parts of organic substance will be used. In the case of rubber, an amount of the order of 0.05 to 5.0 parts per 100 parts of rubber will be sufficient to give excellent resistance to oxidation.

The compounds of the present invention are eifeetive antioxidants for natural rubber or any synthetic rubber which is normally subject to deterioration upon contact with oxygen. Examples of such synthetic rubbers include the rubbery copolymers of butadiene and styrene and the rubbery copolymers of butadiene and acrylonitrile.

Rubber antioxidant tests The following tests illustrate the use of compounds of the present invention as rubber antioxidants:

The chemicals from Examples I, II and III, 2- (2 benzothiazylthio) -1,4 dihydroxybenzene, 2- [2-(4,5-dimethy1 thiazy1thio)] 1,4 dihydroxybenzene, and 2-[2-(4-methyl thiazylthio)1-1,4- dihydroxybenzene were tested in a white natural rubber stock of the following composition:

Parts by weight Pale crepe 100 Zinc oxide l0 Lithopone Whiting 60 Zinc laurate 0.5

Sulphur 3.0 Tetramethyl thiuram monosulfide 0.15

The antioxidant was incorporated in the ratio of 1.0 part per 100 parts of rubber. Cures were 50 made for 10, 20 and 30 minutes at 30 pounds steam Analysis Nitrogen Sulfur pressure. Table I shows the tensiles and elongations of these stocks unaged, after aging for Found 5. 9 27,04 nmetY-SiX hours n er 3 0 pounds of oxygen Th f C H O NS; 5.38 26.89 pressure at C. and after aging for forty- 65 eight hours at C. in an air oven.

0 Unaged Heat Aged Oxygen Aged Antioxidant g? '1 E T E T E None 1 0 2, 340 653 660 560 990 510 A (2-(2-benzothiazylthio)-l, l dlhYdIOXY- benzene) "A ,33 650 890 503 1,870 505 B (2-[2-(4, 5-dimethylthiazy1th1o)]-l,

4-dihydroxybenzene) 2,415 660 1,036 540 2,040 610 O (2-[2-(4-methylthiazylth1o)]-1, 4-d1- hydroxybenzene) 0 2,3 655 930 476 1, 950 020 645 700 4% failed e05 340 460 1, 660 546 045 750 405 1., 720 576 636 sso 455 1,810 e00 650 690 500 failed e45 680 42a 1, 480 545 6-55 870 470 1, 660 575 640 940 466 1. 760 610 T-Tensile. EE1ongation.

tained in the three examples cited (mixtures of the monoand di-substituted 1,4-dihydroxybenzenes) and the quinones obtained by oxidation of the primary products are also excellent antioxidants for rubber.

The chemicals of this invention are of value as antioxidants for synthetic rubber. For example, 2-(2 benzothiazylthio) 1,4 dihydroxybenzene, when incorporated into butadiene-styrene copolymer (GR-S) in the ratio of 1.5 parts per 100 parts of polymer, protected the polymer against resinification for eleven hours at 130 C. The control resinified in one and one-half hours.

While the invention has been particularly described fo-r 2-(2-thiazylthio)-1,4-dihydroxyben zenes, it is equally applicable to other quinonemercaptothiazole compounds such as:

2-(2-benzothiazylthi-o) 1,4-dihydroxy-5-methylbenzene 3-(2-benzothiazylthio) 1,4 dihydroxy 2,5-ditertiary-butylbenzene 2-[2-(4 methyl thiazylthio)] 1,4 dihydroxy- 5-methoxybenzene 2 (6 nitrobenzothiazyl 2 thio) 1,4 dihydroxybenzene 2 (6 aminobenzothiazyl 2 thio) 1,4 dihydroxybenzene 2 (6 hydroxybenzothiazyl 2 thio) -1,4-dihydroxybenzene 2-[2-(4-phenylthiazylthio)l 1,4 dihydroxybenzene 2-[2-(4,5 diethyl thiazylthio)] 1,4-dihydroxybenzene The antioxidants of my invention have the great advantage that in addition to their excellent antioxidant properties they do not discolor organic materials upon exposure to light nor do they stain lacquers or cloth with which they come in contact; This is particularly important in the case of use with rubber to make light-colored or white stocks or articles.

The chemicals disclosed herein are the subject matter of my copending divisional application Serial No. 215,860, filed March 15, 1951.

Having thus described my invention what I claim and desire to protect by Letters Patent is:

1. Rubber protected against deterioration by oxygen by 2-[2-(4,5-dimethyl thiazylthio)]-1,4- dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

2. Rubber protected against deterioration by oxygen by 2-[2-(4-methyl thiazy1thio)]-1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per parts of rubber.

3. Rubber protected against deterioration by oxygen by 2- (2-benzothiaz'ylthio) -1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

4. Natural rubber protected against deterioration by oxygen by 2-[2-(4,5-dimethyl thiazylthio) ]-1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

5. Natural rubber protected against deterioration by oxygen by 2-[2-(4-methyl thiazylthio) 1,4 dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

6. Natural rubber protected against deterioration by oxygen by 2-(2-benzothiazylthio) -1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

7. Rubber protected against deterioration by oxygen by a 2-(2-thiazylthio) -1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

8. Natural rubber protected against deterioration by oxygen by a 2-(2-thiazylthio)-1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of rubber.

9. Rubbery butadiene-styrene copolymer protected against resinification upon exposure to oxygen by a 2-(2-thiazylthio) -1,4-dihydroxybenzene uniformly distributed therethrough in an amount ranging from 0.05 to 5 parts per 100 parts of said copolymer.

THOMAS H. NEWBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,169,717 Young Aug. 15, 1939 2,186,419 Mathes J an, 9, 1940 2,280,792 Brunson. Apr. 28, 1942 2,387,499 Daly Oct. 23, 1945 

1. RUBBER PROTECTED AGAINST DETERIORATION BY OXYGEN BY 2-(2-(4,5-DIMETHYL THIAZYLTHIO))-1,4DIHYDROXYBENZENE UNIFROMLY DISTRIBUTED THERETHROUGH IN AN AMOUNT RANGING FROM 0.05 TO 5 PARTS PER 100 PARTS OF RUBBER. 